The development of digitized time division general telephone networks has resulted in a need to apply pulse-code modulated (PCM) information transmission methods to individual networks. In these networks, however, the typical 30-channel frame PCM structure produces structural problems and problems related to the quality of information transmission. If, e.g., it is desirable to branch fewer than 30 channels at some intermediate station of such an individual network, all of the 30 channels must be decoded to voice frequency signals and the branching must be performed by connections of these channels, which carry voice frequency signals. Up to three channelling devices must be provided at the station if the branched channels are to be transmitted to another station in digital form. If the channels must be decoded and coded again in this way at each intermediate station, interchannel crosstalk, changes in signal level, and noise may accumulate to disturb the transmission. Moreover, such a branching is quite expensive because of difficulties in installation and the large quantity of equipment required.
A particular problem in relation to individual networks is that the intermediate stations must be connected to both of the terminal stations. Under these circumstances, providing a single branch is not sufficient; but it must also be possible to use the transmission capacity of the main line thereby liberated to serve the connections between the particular intermediate station and the other terminal station.
It is an object of the present invention to provide a device for resolving the aforementioned problems and for performing the branching completely digital.